Studies On Effects Of Exogenous Polyamine On Reactive Oxygen Species And Respiratory Metabolism In Cucumber Seedlings Under Hypoxia Stress

In soilless culture, O₂ deficiency in the root-zone is usually thought be a major adverse effect on plants growth and development. This has been an urgent problem that should be solved in soilless culture. Polyamines, mainly including putrescine (Put), spermidine (Spd), spermine (Spm), are ubiquitous lowmolecular aliphatic amines generated in organism metabolism. Many evidences have showed that polyamines are associated with plants growth, differentiation, senescence and responses to stress. Under many kinds of stress conditions, Polyamine content in plants changes rapidly. However, little is known about their physiological relevancy in plants subjected to hypoxia stress.In the present experiment, by using polyamines and polyamine synthesis inhibitor, the effects of polyamines on hypoxia tolerance of cucumber (Cucumis Sativus L.) cultivar seedlings were investigated under hypoxia stress in nutrient solution in which dissolved oxygen precisely controlled through dissolved oxygen controller. Hypoxia-tolerance cucumber cultivars 'Lubachun No.4' and hypoxia-sensitive cultivars 'Zhongnong No.8' were choose as experimental materials. The relationship between polyamines and seedling growth, reactive oxygen metabolism, respiration metabolism and carbohydrate content in cucumber seedlings were discovered, and the physiological regulation role of polyamines in adaptation to hypoxia stress was discussed. Main research results were as follows:Under hypoxia treatment, the contents of free, conjugated, bound polyamine in leaves and roots of two cucumber cultivars seedlings increased with different degrees. The ratio of (free-Spd+free-Spm)/free-Put in 'Lubachun No.4' seedlings was higher than that in 'Zhongnong No.8' seedlings. Compared to the hypoxia treatment, exogenous Spd treatment increased the contents of free-Spd and free-Spm, decreased the free-Put content while increased the contents of conjugated, bound polyamine content with different degrees in leaves and roots, and improved the seedling growth significantly. D-Arg treatment decreased all kinds of polyamine content in leaves and roots significantly, and MGBG treatment decreased contents of Spd and Spm while increased Put content, and each of these treatments decreased seedling growth significantly when compared to the hypoxia...